1. Field of the Invention
The invention relates to arrangements for providing a seamless, integrated network that combines advantages of high data rates, wide area coverage, robustness and mobility support. More specifically, the invention relates to combined networks that seamlessly overlay optical (for example, FSO) and radio frequency (for example, WiMAX) networks, taking advantages of the best features of each technology.
2. Related Art
Free space optics (FSO) and WiMAX communication technologies are known in the art.
FSO involves transmission of low-powered multi-wavelength laser beams through the atmosphere, sending optical signals through the air using lenses and mirrors to focus and redirect the beams. Whereas FSO supports extremely high data rates, it is a line-of-sight (LoS) technology, so that atmospheric conditions such as fog, rain, heavy snow, and other airborne particulates clouds can hinder or bring down FSO transmissions. Moreover, the range of FSO signals is limited as compared to radio frequency (RF) technologies. Further, FSO is generally a point-to-point (PtP) technology, that, especially coupled with its LoS characteristics, have traditionally made it difficult to use with mobile transceivers.
In contrast, Worldwide Interoperability for Microwave Access (IEEE 802.16, or WiMAX,) is a point-to-multipoint (PtM) broadband wireless network communications standard. Essentially a wireless metropolitan area network (WMAN) radio frequency (RF, especially microwave) technology, WiMAX can, for example, connect IEEE 802.11 (WiFi) hotspots to the Internet. WiMAX-compliant stations can have a 50-km communications radius, and so can provide a unified metropolitan area network and allow true wireless mobility without the limitations of WiFi's “hot-spot hopping.” Advantageously, WiMAX allows subscribers connectivity without a direct line of sight (LoS) to a base station and is thus a non-LoS (NLoS) technology. However, WiMAX is characteristic of RF technologies in that its data rate is lower than optical systems.
It is known in the art to hybridize optical and RF technology, but apparently, only in a rudimentary or piecemeal way. U.S. Pat. No. 6,763,195 (Willebrand et al.) discloses a hybrid communication link in which an optical link provides a primary data path, and in which an RF link provides a concurrent or backup path for the network data as well as a reliable and primary path for the control and status information. U.S. Pat. No. 6,725,160 (Johnson et al.) discloses a system for measuring performance of FSO and wireless HF in different stressor (weather) conditions, which “could be designed to test various communication systems during various weather conditions to find optimum technologies and equipment for each of the weather conditions. In some cases, a hybrid system can be developed that combines these optimum systems, and that subsequently uses the optimum system based on the actual weather conditions in the field.” U.S. Patent Application Publication No. 2002/0122230 (Izadpanah et al.) discloses a hybrid wireless and optical communication link having a controller that responds to atmospheric conditions and causes switching between a laser portion and an RF portion. However, none of the conventional systems make use of the best features of both optical and RF technologies, and none provide a seamless network overlaying optical and RF technologies.
The inventors have realized that it would be desirable to combine, in a single network, the high data rate capability of FSO with the range, coverage, robustness and mobility support of WiMAX. However, conventional arrangements have not provided these combined advantages in a seamless, unified network solution. Therefore, there is a need in the art for an arrangement that combines optical data transmission rates, with the range, coverage, robustness and mobility support of RF (for example, WiMAX) networks.